We cannot edit templates or themes. If the theme is not coded to provide footer widgets areas then purchasing a custom design upgrade and CSS editing won't achieve that. Please read this entire section and note the following:http://en.support.wordpress.com/custom-design/#frequently-asked-questionsDoes the Custom Design upgrade let me edit HTML?
No. The Custom Design upgrade allows you to edit fonts and CSS only. You can change the appearance of a theme, but not its HTML markup, PHP code, or content. You can choose to apply your custom fonts or custom stylesheet to any of the themes available on WordPress.com. Some themes, like the plain but versatile Sandbox and Toolbox, are blank canvases waiting for your custom fonts, CSS and images.